..which goes through some numbers and shows that, under the provisions of a bill which passed the Oregon House Transportation and Economic Development Committee on April 4th, a mileage tax would be established for electric vehicles that would effectively tax them at a higher rate than efficient gas-powereed cars.

That's just seems crazy. Good old ODOT??

Phil Covington's post shows some good calculations to back up his reflections. I'd like to take the analysis further.

The huge, giant, tremendous thing that has been missing from discussions I've seen of this EV tax idea relates directly to this common assumption:

"after all, they are road users too, and that infrastructure has to be paid for..."

Here's the thing. The rule of thumb among civil engineers, roughly accurate, is that roadway damage - the main wear and tear from driving - goes by the fourth power of the axle loading.

To work this through, at the Oregon DOT truck load limit, representing a fully loaded truck at 80,000 pounds gross (or a smaller heavy truck depending on configuration), the axle loading can be 20,000 pounds. With a curb weight of about 3500 pounds, a generous estimate for a four-passenger electric sedan might be an axle loading as high as 2000 pounds.

Using those values, the ratio of axle loading between truck and car is 20,000:2,000, or 10:1.

Then, with road wear at the fourth power, the ratio of road wear per mile between truck and car is 20,000^4:2,000^4, or 1.6e+17:1.6e+13, or 10,000:1.

Yes, that is ten thousand to one.

In other words, one fully loaded semi-trailer truck - just one - causes as much road wear per mile, as about 10,000 electric cars.

To help grasp this, visualize a one mile test strip of state highway. Drive one fully loaded semi-trailer truck over it, once. That causes a certain amount of wear.

To cause the same amount of wear to that one mile test strip with electric cars, you'd have to drive back and forth over it 10,000 times.

This is the conclusion that is driven by these numbers:

The road wear caused by electric cars - and by hybrids, and other high-mileage gas-powered cars - all put together - is actually negligible compared to the road wear caused by heavy trucks.

What does that mean about the EV tax proposal?

Given the gas tax structure, it appears that there's a big dirty secret - that passenger cars already very, very heavily subsidize the road wear caused by heavy trucks.

Extending that huge, hidden, market-distorting subsidy forward to burden electric cars is, well... not a very good idea.

Life-cycle costing and carbon-costing of roadway systems may show that reducing maximum vehicle weights - which are huge in the US compared to many other wealthy countries - can be a significant source of economical carbon savings across the system. And on local roads, where institutional vehicles (government, transit, and utilities) may be a large share of the heavy vehicles, this solution may be pursued voluntarily.

In the case of a mileage tax for electric cars, we're not just looking at something badly regressive in terms of important shared objectives - it looks a lot like an attempt to perpetuate a hugely unfair and deceptive highway funding model onto a new, undeserving generation.

An obvious alternative approach to highway funding would be to gradually raise the fees for heavy truck traffic, until it pays something close - at least remotely close - to its share of costs.

The revenue projection in CBO report appears to be based on assumptions of a more-or-less unchanging general approach to transportation over the next 30 years. Given the changes needed to address our enormous greenhouse gas pollution in the U.S., that kind of baseline assumption looks pretty ludicrous.

As a result, the report looks like an exercise in counting the chairs to make sure there are enough places to sit on deck, while the ship whose deck it is, is sinking.